Diversification, Faunal Change, and Community Replacement during the Ordovician Radiations

Abstract

The Ordovician evolutionary radiations represent a major pivotal point in the history of life on earth. During the few tens of million years between the ends of the Cambrian and Ordovician Periods, the nature of marine faunas was almost completely changed. The trilobite-dominated communities of the Cambrian were replaced by complex suspension-feeding communities dominated by brachiopods, bryozoans, and pelmatozoans, and taxonomic diversity, as seen at both local (i.e., community-wide) and global (i.e., worldwide) levels, was increased two- to threefold. These new faunal patterns then persisted with only minor change for the next 200 m.y. of the Paleozoic. Only two other events in the history of marine faunas had comparable importance: the Vendian to Early Cambrian radiations, which emplaced the first marine fauna, and the Late Permian extinctions, which destroyed the Paleozoic fauna established during the Ordovician and led to the subsequent dominance of the modern marine fauna.

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